Magnetic field detecting system

ABSTRACT

4. IN A MAGNETIC FIELD TESTING SYSTEM OF THE TYPE EMPLOYING AN INDUCTANCE BRDIGE OF WHICH AN UNBALANCE THEREIN IS A MEASURE OF THE DEVIATION OF THE MAGNETIC FIELD UNDER TEST FROM A PREDETERMINED VALUE. THE COMBINATION OF AN ALTERNATING CURRENT GENERATOR FOR SUPPLYING EXCITING CURRENT TO SAID BRIDGE AND AN AMPLITUDE REGULATOR FOR CONTROLLING THE AMPLITUDE TO SAID EXCITING CURRENT, SAID COMBINATION COMPRISING A FIRST ELECTRON DICHARGE DEVICE, AN INDUCTIVE WINDING CONNECTED IN THE SPACE-DISCHARGE PATH OF SAID FIRST DEVICE AND INDUCTIVELY COUPLING SAID BRIDGE TO TRANSFER ENERGY THERETO, A PARALLEL TUNED RESONANT CIRCUIT INDUCTIVELY COUPLED TO SAID WINDING, CIRCUIT MEANS INCLUDING SAID INDUCTIVE WINDING AND SAID RESONANT CIRCUIT OPERATIVELY ASSOCIATED WITH SAID FIRST ELECTRON DISCHARGE DEVICE TO FORM THEREWITH AN OSCILLATOR FOR GENERATING ALTERNATING CURRENT AND CAUSING SAME TO APPEAR IN SAID RESONANT CIRCUIT, THE FREQUENCY OF SAID ALTERNATING CURRENT BEING DETERMINED BY THE INDUCTIVE IMPEDANCE OF SAID INDUCTANCE BRIDGE IN CONJUNCTION WITH THE PARAMETRIC VALUES OF SAID WINDING AND SAID RESONANT CURCUIT, A NORMALLY DISABLED GRID-CONTROLLED ELECTRON DISCHARGE DEVICE HAVING ITS ANODE   DIRECTLY CONNECTED TO ONE SIDE OF SAID RESONANT CIRCUIT AND THE CATHODE DIRECTLY CONNECTED TO THE OPPOSITE SIDE OF SAID RESONANT CIRCUIT, CONDUCTION OF SAID GRID-CONTROLLED DEVICE BEING EFFECTIVE TO PROVIDE A LOAD SHUNTING SAID RESONANT CIRCUIT TO THEREBY DRAW CURRENT THEREFROM SO AS TO CONTROL THE AMPLITUDE OF THE GENERATED ALTERNATING CURRENT, CIRCUIT CONNECTIONS FOR MAINTAINING THE ANODE AND CATHODE OF SAID GRID-CONTROLLED DEVICE AT THE SAME D-C POTENTIAL LEVEL IN THE ABSENCE OF ALTERNATING CURRENT IN SAID RESONANT CIRCUIT, SAID CIRCUIT CONNECTIONS ENABLING THE PRESENCE OF ALTERNATING CURRENT IN SAID RESONANT CIRCUIT TO ESTABLISH A POTENTIAL DIFFERENCE BETWEEN SAID ANODE AND SAID CATHODE, AND ALTERNATING CURRENT TRANSLATING MEANS FOR APPLYING THE POTENTIAL OF THE GENERATED ALTERNATING CURRENT APPEARING IN SAID RESONANT CIRCUIT TO THE CONTROL GRID OF SAID GRID-CONTROLLED DEVICE FOR RENDERING SAID GRIDCONTROLLED DEVICE CONDUCTIVE WHEN THE AMPLITUDE OF THE GENERATED ALTERNATING CURRENT EXCEEDS A PREDETERMINED AMPLITUDE VALUE WHEREBY SAID GRID-CONTROLLED DEVICE CONTROLS THE AMPLITUDE OF THE GENERATED ALTERNATING CURRENT.

Feb. 16, 1971 J. a. TATE, JR,, ETAL 3,564,603

MAGNETIC FIELD DETECTING SYSTEM I L IOI 99 93 Filed Aug. 26, 1954 8g L. Wli'ralh United States Patent i 3,564,603 MAGNETIC FIELD DETECTING SYSTEM Joseph B. Tate, Jr., and Louis W. Erath, Washington, D.C., assignors to the United States of America as represented by the Secretary of the Navy Original application Oct. 8, 1945, Ser. No. 621,155. Divided and this application Aug. 26, 1954, Ser.

Int. Cl. H03b 3/02 US. Cl. 331-183 6 Claims This invention relates generally to a depth charge firing control system in which the depth charge is fired in response to predetermined changes in the scalar value of the ambient magnetic field detected by the depth charge as it moves within the vicinity of a submarine to be destroyed thereby, it being well known that the presence of a submarine, or other ponderous mass of magnetic material, within the earths magnetic field causes the ambient field of the depth charge to be altered or changed as the depth charge changes its position with respect to the submarine. 'More particularly, this invention is directed to a novel oscillator to be used in the aforedescribed depth charge firing control system.

This application is a division of copending application, Serial No. 621,155, filed Oct. 8, 1945 and now Patent No. 3,162,119.

In accordance with the control system of the present invention, the depth charge is caused to be fired when the scaler value of the ambient field changes by a predetermined amount first in one direction as the depth charge moves within the vicinity of a submarine and thereafter changes by the same amount in the opposite direction. Firing of the depth charge in response to such changes in the value of the field is accomplished by means of a control circuit including a pair of electronic control channels, one of which is rendered responsive to an increase in the scalar value of the ambient field and is actuated when the scalar value has increased by the predetermined amount. The other channel similarly is rendered responsive to a decrease in the scalar value of the ambient field and is actuated when the scalar value has decreased by substantially the same predetermined amount. When both channels are actuated, they together produce a voltage adapted to initiate operation of a firing circuit for the depth charge.

The changes in the scalar value of the magnetic field are detected by means of a total field magnetometer having a plurality of matched and orthogonally disposed inductors adapted together to yield an inductance depression substantially proportional to the square of the scalar value of the field, the square law response being obtained when the inductor elements are excited by a pure sinusoidal current of optimum value and when the inductor elements are closely matched and orthogonally disposed with the greatest exactness possible. Thus, when square law response is obtained, small changes in the scalar value of the ambient field produce small increases and decreases in the inductance of the magnetometer in accordance with decreases and increases in the scalar value of the field respectively, the changes in inductance being directly proportional to the product of the small changes in the field and the scalar value of the gradient-free or uniform field. The gradient-free value of the field is that value corresponding to the total strength or scalar value of the earths magnetic field in the zone of the earth in which the depth charge is launched.

The magnetometer is arranged as one leg of an inductance bridge circuit to which the aforesaid exciting current is supplied from a novel oscillator having means associated therewith for controlling the amplitude of the oscillator output whereby the optimum value of the ex- 3,564,603 Patented Feb. 16, 1971 citing current is maintained substantially constant regardless of voltage changes in the power supply for the oscillator and changes in the characteristics of the electron discharge devices comprising the oscillator and its amplitude regulator. The bridge circuit preferably is initially balanced in an external field having a value other than any of the values within the range of the earths magnetic field in order that a null condition of the bridge circuit be not obtained in response to the earths magnetic field. The bridge circuit thus assumes a degree of unbalance in accordance with the scalar value of the ambient field of the detector corresponding to the scalar value of the earths magnetic field in the zone of the earth in which the depth charge is launched. The unbalance of the bridge thereafter is altered further to a greater or lesser degree in accordance with changes in the scalar value of the ambient field as the depth charge moves within the vicinity of a submarine, the output of the bridge thus providing an electrical signal which varies in value in accordance with changes in the scalar value of the field.

When sqaure law or quadratic response is obtained from the magnetometer detector, the depth charge associated therewith may be moved angularly about within the gradient-free or uniform magnetic field of the earth without producing spurious signals indicative of apparent changes in the ambient field of the depth charge. Due to the variable character of the detector impedance, however, harmonic frequency voltage components appear across the magnetometer inductors: which cause harmonic frequency currents to flow in the bridge circuit. Harmonic frequency currents flowing in the bridge current intermodulate and produce changes in the amplitude of the fundamental frequency current such that the square law response is impaired. Means, therefore, are provided in the bridge circuit of the present invention to reduce the fiow of harmonic frequency currents to a minimum and to otherwise improve the quadratic response of the detector. Means also are provided in the aforesaid electronic control channels for filtering spurious signal components resulting from non-quadratic response however caused.

Power is supplied to the filaments of vacuum tubes comprising the aforesaid electronic control circuit when the depth charge becomes immersed in water upon launch ing thereof, and the increase in various voltage values throughout the control circuit, as the vacuum tubes thecome actuated, appear as spurious signals which would be adapted, unless substantially eliminated, to effect various operations in the control circuit, these operations, undef certain conditions of operation, being sufiicient to fire the depth charge. These voltages also would prevent rapid stabilization of the control circuit in time to render it responsive to a submarine submerged at a shallow depth. Accordingly, means are provided for discriminating against such spurious signals resulting from arming operations of the control circuit. The character of the control circuit also is such as to make operation thereof possible in response to sudden impulses of pressure received through the water such, for example, as those resulting from countermine shocks. Accordingly, means also are provided in the control circuit for preventing operation of the circuit in response to countermine shocks received by the depth charge and for rapidly restoring sensit'vity of the depth charge after such shocks have been received.

An object of the present invention is to provide a new and improved firing control system for a depth charge in which the depth charge is fired in response to predetermined changes in the scalar value of the ambient magnetic field within which it moves subsequent to launching thereof.

A primary object is to provide an oscillator having new and improved means for maintaining the amplitude of oscillation thereof substantially constant.

Still other objects, advantages and features of the present invention are those implied from or inherent in the novel combination and arrangement of parts as will become more clearly apparent as the description proceeds, reference being had to the accompanying drawings wherein:

The FIG. 1 is a diagrammatic view of a complete electrical circuit of a depth charge firing control system.

Referring now to FIG. 1, it will be seen that magnetometer detector 37 comprises three pairs of matched,

permalloy core coils X. Y and Z disposed respectively in three mutually perpendicular planes in accordance with the arrangement of the total field magnetometer disclosed in the copending application of Everett M. Hafner for Magnetometer, Serial No. 609,307, filed Aug. 6, 1945 and now abandoned.

The permalloy core coils or inductor elements are so constructed that each element yields an inductance depression which is proportional to the square of the component of an external magnetic field parallel to the magnetic axis thereof when the element is excited by a pure sinusodial current of optimum value. The coils are connected in series and the coils lying in the same plane are connected with opposed magnetic polarities such that even harmonic frequency voltages generated by the coils due to the variable character of their impedances cancel, thereby to substantially eliminate the flow of even harmonic frequency currents in the coils. Thus, the elements together yield an inductance depression which is substantially proportional to the square of the scalar value of an external magnetic field when the series connected elements are excited by a common sinusoidal current of optimum value.

The foregoing proportionality may be expressed by the following equation:

where AL=the inductance depression L =the inductance of the detector for zero external field L=the inductance of the detector for a total field of scalar value H K, K K ar proportionality factors H=the scalar value of the total external field.

For a fixed value of sinusoidal exciting current, K, K and K are constants, being functions of the exciting current. Over a limited range of field strength H such, for example, as the range of values of the earths magnetic field, K and K are of such small value that Equation 1 maybe written AL=KH2 Thus, the inductance depression for limited ranges of field strengths is substantially proportional to the square of the scalar value of the external field. Differentiating Equation 2 gives (3) d(AL)=d(L -L)=dL=2KHdH Accordingly, it is seen that small changes in inductance are proportional to the product of the scalar value of the field and small changes therein.

Detector 37 is arranged as one leg of an inductance bridge circuit which includes as its second leg a balance element 52 for the detector. By reason of the variable character of the impedance of the detector, the inductance thereof also varies in response to changes in the bridge current due to variations in the bridge supply voltage, thus producing unbalance of the bridge circuit as the value of the bridge current changes. To compensate for such unbalance, balancing coil 52 also is provided with a permalloy cored coil such that the inductance of coil 52 varies in the same manner as that of the detector in response to variations in the bridge current, thus preventing changes in the degree of unbalance of the bridge circuit due to changes in the bridge current. Coil 52, however, is provided with a permalloy shield designated 53 for preventing variations in the inductance of the coil in response to changes in the external field.

The third and fourth legs of the inductance bridge comprise matched portions of a secondary winding 54 of an iron core transformer generally designated 55. The bridge circuit also includes matched windings 56 and 57 of an iron core transformer generally designated 58, Windings 56 and 57 being employed for the purpose of presenting a high impedance to the flow of harmonic frequency currents in the bridge circuit. Harmonic frequency currents flowing in the bridge circuit intermodulate and produce a distortion of the output of the bridge circuit. Use of windings 56 and 57 in the bridge circuit also makes the total impedance of the circuit large as compared to impedance changes produced therein by variations in the inductance of detector 37. Accordingly, such impedance changes produce relatively small changes in the value of the exciting current supplied to the bridge circuit.

The bridge circuit further includes resistors 59 and 61 for providing a resistance balance therein. The output circuit of the bridge circuit includes a condenser 62, iron core inductance coil 63, resistance 64 and a voltage source generally designated 65. The voltage source includes a potentiometer 66 which is connected in a closed circuit with secondary Winding 67 of transformer 58. The voltage developed across the portion of the potentiometer between the wiper thereof and resistor 64 is used to provide the desired degree of balance in the bridge circuit, and resistor 64 is varied, as is desired, to vary the sensitivity of the bridge output circuit. Condenser 62 and coil 63 together with the bridge inductance as seen from its output are tuned to provide series resonance whereby the impedance to the flow of current through the output circuit is entirely resistive in character and a voltage appears across condenser 62 which is many times the value of the voltage which appears across the output of the bridge circuit between the center tap of winding 54 and the wiper of potentiometer 66. Thus, considerable gain is realized from the resonant circuit.

The voltage appearing across condenser 62 provides an electrical signal which varies in value in accordance with changes in the scalar value of the external ambient field of the detector, the bridge being balanced at any convenient value of an external magnetic field such that a desired degree of unbalance is obtained in response to the scalar value of the earths magnetic field in the region of the earth in which the detector is employed.

As set forth hereinbefore, one of the conditions for quadratic response is that the bridge circuit be supplied with a pure sinusoidal current of optimum value. This current is supplied by the oscillator of the present invention which includes a conventional pentode vacuum tube 68. The plate circuit for tube 68 is supplied from battery 40 and is completed therefrom by Way of conductor 69, plate load resistor 71, the right hand portion, as viewed in the drawing, of primary winding 72 of transformer 55, plate 73 and cathode 74 of tube 68, conductor 70, hydrostatic switch 75 and thence by way of conductor 76 to ground potential at tap 77 of battery 40. Screen grid 78 of tube 68 receives its operating potential from conductor 69 by way of resistor 79 and is coupled to ground potential through switch 75 by means of the conventional A.C. bypass condenser 81. Control grid 82 of tube 68 normally is maintained at a negative potential with respect to ground by reason of its connection with battery tap 83 by way of conductor 84 and resistors 85 and 86. Voltage also is applied to control grid 82 from conductor 69 by way of a circuit'including resistor 71, the left hand portion of winding 72, as viewed in the drawing, condenser 88, resistor 86 and thence by way of condenser 87 and conductor 70 to ground potential through switch 75. The voltage thus applied to control grid 82 from load resistor 71 and winding 72 is substantially out of phase with the voltage applied to plate 73 from load resistor 71 and the winding and, accordingly, operation of oscillator tube 68 is inherently regenerative in character. Resistor 71 provides negative feedback in proportion to the flow of current therethrough and thus tends to sabilize the frequency and amplitude of oscillation of the oscillator. Condenser 87 serves to eliminate parasitic oscillations at a high order of frequencies for the reason that it provides a bypass for voltages at such frequencies.

The oscillator is turned to a desired frequency such, for example, as 3000 cycles per second by the selection of the value of condenser 89 in relation to the combined inductive effects of windings 54, 72 and 91 of transformer 55 and the inductive effects of the bride circuit including magnetometer detector 37, condenser 89 preferably being connected across winding 91, as shown. The oscillator builds up at this frequency to the desired amplitude of oscillation due to its inherent regeneration, and is limited at the desired amplitude by means of a regulator tube 92 together with its associated circuit elements. Tube 92 may be a conventional amplifier vacuum tube of any type, but preferably includes a diode section for reasons hereinafter to appear.

The plate circuit for tube 92 may be traced from winding 91 of transformer 55, plate 93 and cathode 94 of tube 92, conductor 70, hydrostatic switch 75 and thence by way of conductor 76 at ground potential on the other side of winding 91, screen grid 95, in this case, being connected to plate 93. Control grid 96 of tube 92 is normally biased at a negative potential such, for example, as 96 volts negative with respect to ground potential at tap 77 of battery 40 and is connected to the low potential side of the battery by way of conductor 97 and resistor 98. The control grid also has voltage applied thereto from secondary winding 91 of transformer 55 by way of a grid circuit including resistor 99, resistor 101 and varistor 102 in parallel, and thence by way of condenser 103 to grid 96. By reason of the large negative bias on control grid 96, the amplifier section of tube 92 conducts only during peak portions of positive half cycles of the AC. voltage applied to the control grid. However, when the voltage across winding 91 reaches such a value that the negative voltage on the control grid is reduced to a predetermined value, sufiicient energy is drawn by the tube from the tuned circuit of the oscillator, thereby rendering tube 68 less regenerative in operation and thus causing a reduction in the voltage across windings 54, 72 and 91. Thus, the optimum value of the voltage supplied to the bridge circuit including winding 54 is maintained substantially constant. This voltage is held within very close limits for the reason that small percentage changes in the AC. voltage at grid 96 of regulator tube 92 produce relatively large percentage changes in the flow of current through the tube. Varistor 102 is employed for the purpose of compensating for variations in circuit parameters with temperature. This is accomplished by causing the voltage division in the grid circuit to vary as the Varistor changes value in response to the temperature variations. Resistor 99 is initially selected of such value as to provide a desired voltage division in the grid circuit.

The electrical signal appearing across condenser 62 is applied to the control grid 104 of a conventional pentode amplifier vacuum tube 105, the control grid being normally biased at a negative potential with respect to ground potential by reason of its connection to conductor 84 by way of inductance 63 and the bridge circuit. The plate circuit of tube 105 is supplied from battery 40 and may be traced from the high potential side thereof by way of conductor 69, primary winding 107 of transformer 108, plate 109, cathode 111, and thence by way of winding 112 of transformer 108 to ground potential at conductor 76 by Way of conductor 70 and switch 75 in parallel with winding 114 of transformer 108 which is connected by way of conductor 115 and an incandescent lamp 116 to battery tap 117 which is at a positive potential with respect to ground at tap 77. The voltage developed across winding 112 is applied to the cathode with such polarity with respect to the polarity of the voltage applied to the plate from primary winding 107 that degenerative feedback is provided for tube 105, thereby to stabilize the operation thereof substantially instantaneously in order to avoid drift at the input of the amplifier. Drift would produce voltages in the output of the amplifier, which voltages would appear as apparent signals. Cathodes 111, 74 and 94 of tubes 105, 68 and 92 respectively are of the filament type and receive their energy from tap 117 by way of lamp 116 and conductor 115. Lamp 116 is employed for the purpose of providing rapid heating of the filaments with a subsequent reduction in the filament voltage. This is accomplished by use of the lamp for the reason that its resistance varies with temperature.

The amplified output of tube appears across secondary winding 121 of transformer 108, and a condenser 122 is connected thereacross to tune the secondary winding in order to provide proper impedance matching with the tube. The voltage appearing across winding 121 is applied to a pair of electronic control channels adapted to respond to increases and decreases in the voltage, which increases and decreases correspond to signals received in response to variations in the scalar value of the field. These channels are identified by series connected copper oxide rectifiers 123 and 124 individual to one of the channels and similar rectifiers 125 and 126 individual to the other of the channels.

Rectifiers 123 and 124 are connected to Winding 121 with polarities opposite to those of rectifiers 125 and 126, the polarities of the rectifiers being established by reason of their connections with Winding 121. Thus, condenser 127 associated with rectifiers 123 and 124 of one of the control channels is charged substantially to the positive peak value of the steady state or no signal voltage appearing across winding 121. Similarly, condenser 128 associated with rectifiers 125 and 126 in the other control channel is charged substantially to the negative peak value of the steady state voltage appearing across winding 121.

Parallel connected condensers 129 and 131 also are charged to the potential across condenser 127 by way of resistor 130, the low potential side of condensers 129 and 131 being at ground potential when the condensers are fully charged for the reason that resistor 130 is connected to winding 121 at ground potential on conductor 76. When a signal corresponding to a decrease from the steady state value of the voltage appearing across winding 121 is received, condenser 127 discharges by way of resistor 132 connected thereacross, and condensers 129 and 131 discharge by way of resistors 132 and 130, thus producing a voltage across resistor 130 which is negative with respect to ground potential. Similarly, when a signal corresponding to an increase in the voltage across winding 121 is received, a voltage which is positive with respect to ground potential is developed across resistor 130. In either case, high frequency components appearing as ripples in the signal voltage are attenuated by means of condenser 133 whereby such voltage components do not effectively change the potential across condenser 133 with respect to ground potential. Condenser 134 likewise serves to attenuate signals which change in value more rapidly than those within a predetermined frequency range determined by the rate of change of the scalar value of the ambient magnetic field, which rate of change in turn is controlled by the rate of change of position of the depth charge with respect to the submarine. The signals desired to be attenuated are those produced, for example, by excessive angular movement of the depth charge within the ambient magnetic field thereof.

When the signal is in the predetermined range of fre quency, the nezative voltage developed across resistor 130 is applied by way of resistors 135 and 136 to the control grid 137 of a conventional diode-pentode vacuum tube 138 whose operating potential is controlled through adjustment of the potential on its screen grid 139, as will be described in greater detail hereinafter. The operating point of the tube, however, is such as to render the tube conductive when the control grid thereof is at ground potential, thereby causing the plate of the tube to assume a low potential with respect to the voltage at the high potential side of battery 40, which battery potential may be in the order of 135 volts. It is desirable that the plate voltage for such value of grid potential be in the order of 30 volts in order that the plate voltage may increase over a wide range in response to a negative signal applied to the grid and may decrease by a limited and substantially small amount in response to a positive signal applied thereto. The plate circuit of tube 138 may be traced from conductor 69 by way of plate load resistor 142, plate 141, and cathode 143 of tube 138 and thence by way of conductor 70 through switch 75 to ground potential at conductor 76. Thus, as the negative potential is applied to control grid 137, the plate potential rises in proportion to the decrease in the flow of current through the plate load resistor 142 and tube 138, thereby providing a voltage pulse of relatively great amplitude at the plate of the tube corresponding to the signal applied to the control grid thereof. As will appear more fully hereinafter, this voltoge pulse is employed to fire a gas type trigger tube which, in turn, is utilized together with a similar trigger tube individual to the other of the control channels to control the firing circuit of the system.

When the received signal is of such polarity as to develop a positive voltage of sufiicient amplitude across resistor 130 such as occurs principally during arming of the control circuit, the larger portion of the charging current of condensers 129 and 131 passes by way of resistor 135 through the diode section of tube 138, the diode section including plate 144 and cathode 143 of the tube. The cathode of tube 138 and that of tube 154 of the other control channel are of the filament type and are supplied from conductors 70 and 115 in the same manner as tubes 105, 68 and 92, a resistor 145 preferably being interposed in the filament circuit for tubes 138 and 154 to reduce the filament voltage thereof, whereby tubes 138 and 154 are caused to become activated after tubes 68, 92 and 105. By reason of such arrangement, the possibility of producing a complete operation of either of the control channels in response to arming of the control circuit is substantially reduced. By reason of the voltage on cathode 143, which voltage is above ground potential, the diode section of tube 138 is rendered non-conducting when the voltage at plate 144 thereof drops below the cathode potential. When this occurs, the remaining voltage is dissipated by way of the grid circuit of the tube, the remaining charging current flowing by way of resistor 136 and thence through grid 137 and cathode 143 of tube 138 to ground potential at conductor 70.

The electronic control channel including rectifiers 125 and 126 is generally similar in circuit arrangement to the aforedescribed control channel including rectifiers 123 and 124, this channel also having a pair of condensers 146 and 147 which are charged to the negative potential across condenser 128 and further comprises a 3000 cycle filteringcondenser 148 and a spurious signal filtering condenser 149. Thus, when a signal corresponding to an increase in the steady state voltage across winding 121 is received, a negative voltage with respect to ground is produced across resistor 151, and this voltage is applied by way of resistors 152 and 153 to grid 137 of tube 154. Tube 154 may be identical to tube 138 and accordingly, lik reference characters are employed to designate the same tube elements. As in the case of operation of tube 138, a nega tive voltage applied to the grid of tube 154 decreases the voltage drop across the vplate load resistor 155 therefor, thus elevating the plate potential to provide a voltage pulse of relatively great amplitude sufficient to fire a gas type trigger tube associated therewith in a manner hereinafter to appear.

When the signal is of such polarity as to produce a voltage across resistor 151 which is positive with respect to ground potential, condenser 128 discharges through resistor 156 connected thereacross, and condensers 146 and 147 discharge by way of resistor 151, through ground potential by Way of switch and thence through resistor 156 to the other side of the condensers, thus producing the positive voltage drop across resistor 151. This voltage drop is dissipated by flow of the charging current of condensers 146 and 147 through resistor 152 and thence through the diode section of tube 154 as long as plate 144 of the tube is at positive potential with respect to cathode 143 thereof, the cathode of tube 154 being connected in parallel with that of tube 138.

The operating potentials for screen grids 139 of tubes 138 and 154 are supplied from conductor 69 by way of resistor 157, potentiometer 158 and parallel connected potentiometers 159 and 161, these potentiometers being employed for the purpose of setting and equalizing the no signal operating potentials of the plates of these tubes. By selectively adjusting the potentiometers, a desired and equalized gain for tubes 138 and 154 my be obtained without disturbing the desired operating potentials thereof.

It is desirable that the electronic circuits comprising the control system of the depth charge be rapidly stabilized upon arming of the depth charge as it becomes immersed in water upon launching thereof in order that it be ready to respond to a submarine Within its vicinity. For example, as voltage is developed across condensers 127, 129 and 131 as the vacuum tubes of the system become activated, the charging current to condensers 129 and 131 is rapidly bypassed to ground through the diode section of tube 138, as described heretofore in connection with an increase in the voltage across winding 121 above the steady state value thereof. The negative voltages developed across condensers 128, 146 and 147 and the corresponding voltage drop developed across resistor 151 as the tubes of the system become activated, unless compensated for, is sufficient to produce a voltage pulse at plate 141 of tube 154, which voltage pulse would simulate the voltage pulse produced thereon in response to a negative signal voltage applied to grid 137 of tube 154. The necessary compensation is accomplished by producing a counterpotential of sufficient value to render the control grid 137 of tube 154 positive with respect to ground. The counterpotential is supplied by the voltage developed across condenser 162 which is charged from conductor 69 by way of resistors 163 and 164, condenser 162 and thence by way of resistor 132 to ground potential on conductor 76. When condenser 162 is fully charged, potential on conductor 69 is applied by way of resistors 151, 152, and 153 to grid 137 of tube 154. Thus, as switch 75 is closed upon immersion of the depth charge in water, condenser 162 discharges through neon bulb 165, resistor 166 and thence through resistor 151 and switch 75 to ground potential at conductor 76. The voltage drop thus produced across resistor 151 applies a positive potential to control grid 137 of tube 154 as negative potential is developed across condensers 146 and 147 as the tubes of the system become activated. Potential developed across condenser 127, as the voltage across winding 121 assumes its steady state value, elevate the potential across condenser 162 and thus insures that the positive voltage drop across resistor 151 exceeds the negative potential developed across condensers 128, 146 and 147. When tube 154 becomes activated, condenser 162 thereafter is discharged through the diode section of tube 154 by way of neon bulb 165, resistors 166 and 152 and thence to plate 144 and cathode 143 to ground potential on conductor 70, thus rapidly stabilizing the system and placing it in readiness to respond to signals received from a submarine as the depth charge descends through the Water.

The character of the electronic circuits is such as to make possible the production of voltages in response to countermine shocks, which voltages simulate voltage pulses produced by signals received in response to the presence of a submarine. In order to prevent the development of such signals, an inertia switch 157 adapted to be closed in response to impulses of pressure received through the surrounding water such, for example, as those produced by countermine shocks, is employed to apply battery potential on conductor 69 to control grid 137 of tube 138 by way of switch 167, neon bulb 168, resistor 169 and resistors 135 and 136. Similarly, battery potential on conductor 69 is provided by way of switch 167, neon bulb 171, resistor 172 and resistors 152 and 153 to control grid 137 of tube 154. Concurrently with the application of battery voltage to the control grids of tubes 138 and 154, a condenser 173 is charged from conductor 69 by way of switch 167 and resistor 174. After switch 167 has opened, positive potential is maintained on control grids 137 of tubes 138 and 154 for an interval sutficient to permit the control circuit to stabilize following the countermine shocks by reason of the discharge of condenser 173 by way of resistor 174 and bulb 168, resistor 169 and thence through resistor 130 in parallel with resistors 135 and 136 in the diode and gird circuits of tube 138 respectively. A portion of the current flowing through resistor 174 also flows by way of bulb 171, and resistor 172 and thence through resistor 151 in parallel with the diode and grid circuits of tube 154 to ground potential on the other side of condenser 173. Before condenser 173 becomes fully discharged, h wever, bulbs 168 and 171 extinguish, and complete discharge of the condenser is accomplished by way of resistor 174, resistor 175, conductor i176 and thence by way of plate 177 and cathode 94 of the diode section of tube 92 to ground potential on conductor 70 when switch 75 is closed.

The voltage impulse developed at plate 141 of tube 138 in response to a signal which changes in value in the proper direction, is applied by way of a coupling condenser to the control grid 179 of a cold cathode gaseous discharge type trigger tube 181 whose plate 182 is connected to the high potential of battery 40 on conductor 69 and whose cathode 183 is connected by way of cathode load resistor 184, conductor 185 and thence by way of hydrostatic switch 186 to ground potential on conductor 76. Similarly, the voltage pulse developed at plate 141 of tube 154 is applied by way of coupling condenser 187 to control grid 179 of tube 188 which may be identical to tube 181. Plate 182 of tube 188 also is connected to battery potential on conductor 69 and cathode 183 thereof similarly is completed by way of cathode load resistor 189 and thence by way of conductor 185 and switch 186 to ground potential on conductor 7 6.

Control grids 179 of tubes 181 and 188 are maintained at a fixed bias potential such, for example, as 33 volts by reason of their connection with tap 191 of battery 40, conductor 192 and resistors 193 and 194 connected respectively to the control grids of tubes 181 and 188. Copper oxide rectifiers 195 and 196 are connected across resistors 193 and 194 respectively for the purpose of providing rapid discharge paths for condensers 178 and 187 respectively. These condensers are initially charged to the high potential of battery 40 on conductor 69 before tubes 138 and 154 are rendered conducting. When the tubes become conductive and the plate voltages thereof are reduced in an amount such, for example, as 30 volts, condensers 178 and 187 discharges by way of tubes 138 and 154 respectively, the return paths of the condensers being by way of rectifiers 195 and 196' respectively. Condensers 197 and 198 connected across plate load resistors 142 and 155 of tubes 138 and 154 serve as filters to prevent rapid voltage changes across their associated resistors.

When the potential on control grids 179 of tubes 181 and 188 is raised to a value such, for example, as 70 volts, these tubes are rendered conducting, the current discharge through tube 181, for example, flows in part through cathode load resistor 184 and thence to ground through switch 186 and in part by way of resistor 199, copper oxide rectifier 201 and thence by way of cathode load resistor 189 of tube 188 to ground potential on cinductor 185, switch 186 being closed. Similarly, when tube 188 is rendered conducting, the current discharge therethrough flows in part through cathode load resistor 1*89 thereof and in part by way of resistor 200, copper oxide rectifier 212 and thence by way of cathode load resistor 184 of tube 181 to ground potential on conductor 185, switch 186 being closed. The voltage drop thus developed across either of resistors 1184 or 189 depending on whichever of tubes 18 1 or 188 is conducting is applied by way of coupling condenser 202 to control grid 179 of tube 203 which may 'be identical to tubes 181 and 188 and whose plate 182 is connected to battery po tential on conductor 69 and whose cathode 18.3 is connected through hydrostatic switch 204 to one side of an electro-responsive detonator 205. The other side of detonator 205 is connected through hydrostatic switch 206 to ground potential on conductor 76. Control grid 179 of tube 203 is normally biased at a potential such, for example, as 55 volts by reason of its connection through resistor 207 and conductor 208 to battery tap 209. This potential also is applied to cathode 183 of tube 203 by way of resistor 211 before switches 204 and 206 are closed. After these switches close, the cathode is maintained substantially at ground potential, the voltage drop across the detonator being of a low order by reason of the current therethrough which is insufiicient to fire the detonator.

The voltage applied to control grid 179 of tube 203 when either of tubes 181 and 188 are fired is insufficient to elevate the potential on control grid 179 of tube 203 by more than a few volts above the bias potential thereon by reason of the voltage division produced by the cathode load resistor of the nonconducting one of tubes 181 or 188 and either of resistors 199 or 200 associated with the conducting tube, the voltage developed across the cathode load resistor of the nonconducting tube being only a few volts. Use of rectifiers 201 and 212 prevents the voltage division of the potential appearing across the cathode load resistor of the conducting one of tubes 181 or 188 from being such as to elevate the potential on the control grid of tube 203 to such a value as to fire the tube. Thus tube 203 is not fired in response to triggering of only one of tubes 181 or 188. When both of tubes 181 and 188 are fired, however, the cathode potential of the tubes is applied to condenser 202 and elevates the potential on the control grid side thereof sufficiently to render tube 203 conducting whereupon condenser 213 is connected across the high potential side of battery 40 and ground potential at tap 77 thereof is discharged together with battery 40 through tube 203 and detonator 205 thereby to fire the detonator and fire in turn the booster charge 25 and charge 17 of the depth charge. Condenser 213 also serves as a decoupling filter for bypassing A.C. components in the electronic circuits.

A pair of neon bulbs 214 and 215 are connected in series with resistors 216 and 217 respectively across conductor 69 and ground potential on conductor 76 when switch 75 is closed. These bulbs, therefore, are continuously illuminated and provide a source of light for neon bulbs 165, 168 and 171 and trigger tubes 181, 188 and 203, bulbs 214 and 215 for this purpose being mounted in close proximity to the other neon bulbs and the trigger tubes. Such an arrangement is productive of a more efficient operation of the bulbs and tubes, it being well known that the ignition or breakdown potential of such gaseous discharge devices is stabilized by the presence of 1 1 light. The neon bulbs may be of any type suitable for the pupose and preferably are of the type known in the art by the trade name of Tattelite. These bulbs have a high impedance when nonconducting and a low impedance when conducting and, therefore, are well adapted to produce the desired circuit effects when conducting and do not appreciably disturbe the stability of asociated circuits when nonconducting.

A plurality of suitable switches 225, 226, 227 and 228, here shown to be single pole double throw switches are employed for the purpose of converting the control system for the use with depth charges of different structural configurations. The switches, for example, when placed in their dashed-line positions adjust the control circuits associated therewith such that a different predetermined range of frequencies may be effective to produce voltage pulses at the plates of tubes 138 and 154. Such a conversion is desirable for the reason that depth charges of different shapes descend through the water at different rates and thus produce signals of different periods. Also, depth charges of different shapes move angularly about in a different manner in the water during descent therof and therefore produce different frequencies of spurious signals due to the local movement of the depth charges.

From the foregoing, the character and operation of the various electrical components comprising the electrical control circuits of the present invention should now be apparent and further operation thereof merely will be alluded to in the following general statement of operation of the depth charge which, it will be assumed, moves within the vicinity of a submarine after launching thereof. As the depth charge becomes immersed in the water, hydrosatic switches 75, 186, 204 and 206 close as plungers 218, 219 and 221 respectively associated therewith are driven under power of diaphrams 222, 223 and 224 individual thereto, the diaphra-ms in turn being moved in response to the pressure of the surrounding water. After a predetermined interval of time corresponding to the time required for the depth charge to descend through the water to a depth such, for example, as 15 feet, the steady state positive and negative voltages are developed across condensers 127 and 128- respectively.

As the scalar value of the ambient magnetic field of the depth charge varies as the depth charge changes its position with respect to the submarine, the steady state value of the positive and negative voltages changes in one direction or the other and thus produces an electrical signal which causes a voltage pulse to be developed at the plate of either of tubes 13-8 or 154 according to the direction of change of value of the signal. Assuming, for example, that the voltage pulse is developed at the plate of tube 138, this voltage pulse, if of sufficient amplitude, renders tube 181 conductive. If, thereafter, a signal of proper polarity is received to produce a voltage pulse at the plate of tube 154, tube 188 is rendered conductive, thereby to render tube 203 conductive in turn, as set forth in detail hereinbefore. When tube 203 is rendered conductive a circuit is completed for firing the detonator to explode the depth charge as it moves into a position in which it is effective to destroy or damage the submarine.

From the foregoing it should now be apparent that an oscillator for a depth charge firing control system has been provided which is well adapted to fulfill the afore stated objects of the invention.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. In an oscillator arrangement of the character disclosed, the combination of first and second grid-controlled electron discharge devices, a load of predominantly inductive characteristic, circuit means including a source of di- 12 rect current potential operatively associated with the electrodes of said first discharge device to form therewith a regenerative oscillator generating an alternating current for application as exciting potential to said load, said circuit means further including first and second inductive windings and a capacitor, means conductively connecting said first winding in the space discharge path of said first device, said second winding and said capacitor being mutually connected to form a parallel tuned circuit conductively disposed in the space discharge path of said second device, means for mutually inductively coupling said first winding with said load and said tuned circuit whereby said generated alternating current is inductively translated to said load and said tuned circuit, the frequency of said generated alternating current being determined by the combined reactance of said first winding in conjunction with the reactance of said load and said tuned circuit, bias means connected to the control grid of said second device to apply thereto a bias potential of such magnitude as to maintain said second device in a nonconductive condition until the amplitude of the peak portions of the positive half-cycles of the generated alternating current appearing in said tuned circuit exceeds said bias potential by a predetermined amount sufiicient to render said second device conductive whereupon said second device draws current from said tuned circuit to limit the optimum amplitude of the generated alternating current to a predetermined constant level, and electrical elements interconnecting said tuned circuit with the control grid of said second device for applying the alternating current appearing in said tuned circuit to said grid to thereby vary the grid potential in a manner following the amplitude variations of said generated alternating current.

2'. In an oscillator of the character disclosed, the combination of a first grid controlled electron discharge device, means including a tuned circuit for causing said electorn discharge device to oscillate and for rendering the device regenerative in operation, a portion of said tuned circuit being defined by a parallel reactance circuit in which appears the oscillatory energy produced by oscillation of said first device, a second electron discharge device having at least an anode cathode and a control grid, said reactance circuit being connected across said anode and cathode in a manner such that said anode and cathode are at the same DC. potential level in the absence of oscillatory energy in said reactance circuit, means for applying to said control grid a predetermined fixed bias potential which is negative relative to said DC. potential level to thereby maintain, in the presence of oscillatory energy in said reactance circuit, said second device in a normally non-conductive condition until the amplitude of said 0scillatory energy exceeds said fixed bias potential by a predetermined value sufiicient to render said second device conductive, and an R-C network for superimposing the oscillatory energy appearing in said reactance circuit on said control grid to vary the resultant grid potential thereon is a manner following the amplitude variations in the tuned circuit voltage with said fixed bias potential serving as a reference, the presence of oscillatory energy in said reactance circuit providing a potential difference between said anode and said cathode for causing said sec ond electron discharge device to conduct and draw energy from the tuned circuit upon the amplitude of said oscillatory energy attaining said predetermined values thereby to maintain the optimum amplitude of oscillation of the first electron discharge device at a substantially constant value.

'3. In the combination of claim 2 wherein said R-C network includes resistance means and capacitance means serially interconnected between said reactance circuit and said control grid, and a varistor shunting a portion of said resistance means to compensate for variations in circuit parameters due to temperature changes.

4. In a magnetic field testing system of the type employing an inductance brdige of which an unbalance therein is a measure of the deviation of the magnetic field under test from a predetermined value, the combination of an alternating current generator for supplying exciting current to said bridge and an amplitude regulator for controlling the amplitude of said exciting current, said combination comprising a first electron discharge device, an inductive winding connected in the space-discharge path of said first device and inductively coupling said bridge to transfer energy thereto, a parallel tuned resonant circuit inductively coupled to said winding, circuit means including said inductive Winding and said resonant circuit operatively associated with said first electron discharge device to form therewith an oscillator for generating alternating current and causing same to appear in said resonant circuit, the frequency of said alternating current being determined by the inductive impedance of said inductance bridge in conjunction with the parametric values of said winding and said resonant circuit, a normally disabled grid-controlled electron discharge device having its anode directly connected to one side of said resonant circuit and 20 establish a potential difference between said anode and said cathode, and alternating current translating means for applying the potential of the generated alternating current appearing in said resonant circuit to the control grid of said grid-controlled device for rendering said gridcontrolled device conductive when the amplitude of the generated alternating current exceeds a predetermined amplitude value whereby said grid-controlled device controls the amplitude of the generated alternating current.

5. In the combination of claim 4, further including means for applying to said control grid at fixed bias potential which is negative relative to said D-C potential level and which serves as a reference in determining said predetermined amplitude value.

6. In the combination of claim 4, wherein said translating means includes resistance means and capacitance means serially connected directly between said one side of said resonant circuit and said control grid, and a varistor shunting a portion of said resistance means.

References Cited UNITED STATES PATENTS 2,512,658 6/1950 Levy 25036.2S

25 RODNEY D. BENNETT, Primary Examiner S. BUCZINSKI, Assistant Examiner US. Cl. X.R.

presence of alternating current in said resonant circuit to 30 10218; 32443; 33186, 169, 182 

